The invention relates to a process for controlling a start-stop operation of a vehicle having a hybrid drive, as well as to a vehicle which can carry out the process.
Vehicles having a hybrid drive, for example, with an internal-combustion engine as a gasoline, gas or diesel engine, and an electric motor as a synchronous motor, are known in various designs, such as parallel hybrids and series hybrids and include service brake systems with an ABS.
A start-stop operation of a vehicle, particularly in city traffic, for example, at traffic lights or in a traffic jam, necessitates a successive starting and decelerating of the vehicle. During stoppage times of the vehicle, the engine, i.e., the internal-combustion engine, is switched off in order to save fuel and to reduce pollutant emissions. When starting, the internal-combustion engine will then be started and the vehicle will be accelerated until the next deceleration. Start-stop systems for motor vehicles are known in which operating conditions of the vehicle and of the operating pedals are determined and are analyzed for switching off and restarting the internal-combustion engine. This applies especially to vehicles in stop-and-go traffic and particularly to supply and delivery driving, such as mail and parcel services using medium-sized vehicles, in which case a parking brake has to be operated when stopping and has to be released when starting. As a result of the frequent torque—load change in the transmission line, whereby the internal-combustion engine is operated outside its ideal characteristic diagram, high wear, high fuel consumption, as well as a constant uncomfortable operation of the parking brake should be considered to be disadvantages.
It is therefore an object of the present invention to create an improved process for controlling a start-stop operation of a vehicle having a hybrid drive, whereby the above-mentioned disadvantages will be eliminated or considerably reduced and additional advantages will be provided. A further object consists of providing a corresponding vehicle.
According to the present invention, a process is provided for controlling a start-stop operation of a vehicle, which has a hybrid drive with an internal-combustion engine and an electric motor, a service brake with an ABS, and an electric parking brake. The process includes the following steps: (S1) determining, monitoring and analyzing performance parameters of the vehicle, of the internal-combustion engine, of the electric motor, of the service brake and of the electric parking brake, the performance parameters featuring the vehicle speed, the rotational wheel speed, the rotational speeds of the internal-combustion engine and of the electric motor, operations and conditions of a service brake pedal, of a parking brake pedal and of an accelerator pedal; (S2) automatically releasing the electric parking brake in the case of a starting prompt because of determined performance parameters; (S3) driving the vehicle by way of the electric motor for the start; (S4) starting the internal-combustion engine by way of the electric motor if the internal-combustion engine is switched off; (S5) driving the vehicle by way of the electric motor and the internal-combustion engine; (S6) activating a generator operation of the electric motor in the case of a braking prompt because of determined performance parameters; (S7) activating the service brake; and (S8) automatically locking the electric parking brake when the vehicle is stopped after a previously definable deceleration time.
A corresponding vehicle having a hybrid drive with an internal-combustion engine and an electric motor has the following: a service brake with an ABS control unit and a service brake pedal; an electric parking brake with a parking brake control and a parking brake lever; at least one clutch for coupling the internal-combustion engine and the electric motor with the wheels of the vehicle; a hybrid drive control unit for controlling the hybrid drive; and a bus for connecting control units, actuators and sensors of the vehicle and the transmission of control signals. The electric parking brake is connected with the hybrid drive control unit for an automatic controllability in previously definable operating conditions of the vehicle.
As a result of the automatic controllability of the electric service brake when controlling the start-stop operation of a vehicle with a simultaneously adapted control and utilization of the electric motor, it becomes possible to advantageously simplify a starting operation and a stopping operation for the driver in that the operating comfort is increased and the driver's attention is not diverted from the traffic when he leaves the vehicle and starts to drive. In this case, fuel consumption is reduced because the electric motor carries out the starting operation and/or assists the internal-combustion engine.
A start or starting prompt when the vehicle is stopped can be determined by the fact that the brake pedal is released or the parking brake was previously locked and the accelerator pedal is operated, which may, for example, be so in the case of a stop at a traffic light. When the vehicle is stopped, after entering the vehicle, the operation of a starting button or an ignition lock while the accelerator pedal is simultaneously operated may represent a starting prompt. Additional combinations are contemplated.
In the case of a driving vehicle, a braking prompt is generated by operating the service brake pedal or by a corresponding signal of a so-called braking assistant.
In the case of a stop or halt operation, another advantage consists of the fact that the electric motor or the hybrid drive is additionally used as a brake in the event of a braking prompt, a transition taking place for using the service brake. In this case, the electric motor, as a generator, can take over a braking function of the vehicle and can simultaneously convert the braking power to electric power for charging a vehicle battery.
As a result of the detection of performance parameters, it becomes possible to determine whether, after a stopping operation, the vehicle continues to be stopped, in which case, the parking brake will then be locked automatically, which, in turn, represents an operating comfort for the driver and offers additional safety because the parking brake may often be forgotten.
The automatic releasing of the electric parking brake and the driving of the vehicle by means of the electric motor can be carried out simultaneously. This can also increase the operating comfort, particularly in the case of vehicles with a manual transmission, because concentrating on releasing the parking brake and simultaneously starting without having the vehicle roll backwards can be eliminated when starting on a slope.
When the internal-combustion engine is switched off while the vehicle is stopped, a starting of the internal-combustion engine can take place after the expiration of a previously definable time period after the process step of driving the vehicle by using the electric motor. When the internal-combustion engine is still in operation, the electric motor can assist the starting operation, in which case the internal-combustion engine is assisted in such a manner that its efficiency is as high as possible and the fuel consumption is low.
When a braking prompt occurs, the generator operation of the electric motor and the service brake can be activated simultaneously. As an alternative, it is also contemplated that the process step of activating the service brake takes place after the expiration of a previously definable time period after the activating of the generator operation of the electric motor.
It is a special advantage that, when a circuit defect of the service brake is determined in the process step of determining, monitoring and analyzing performance parameters and, while the vehicle is driving, a braking prompt is made by means of the service brake pedal and/or the parking brake lever, the process also features the following process steps for an emergency running function, which is also called “secondary braking I”: (S1.A1) activating a generator operation of the electric motor; (S1.A2) activating the electric parking brake; and (S1.A3) automatically locking the electric parking brake when the vehicle is stopped after a previously definable deceleration time. Also in the case of a defective service brake pedal, an emergency running function (“secondary braking II”) is contemplated, in which case the following process steps take place: (S1.B1) activating operable electric modules of a control unit ABS of the service brake; (S1.B2) activating a generator operation of the electric motor; (S1.B3) activating the electric parking brake; and automatically locking the electric parking brake when the vehicle is stopped after a previously definable delay time.
The operable electric modules may have a reservoir connection for compressed brake control air or compressed brake control operating air, which can be used for an electromechanical controlling of the service brake.
The activation of the generator operation of the electric motor may feature a step-by-step adjusting of the generator operation. Within the range of the stepping capability, a PWM triggering of an actuator system of the parking brake can take place. This actuator system may have a spring-type servo-cylinder (pneumatic or hydraulic in the case of AOH, i.e. air over hydraulic) or may have electromotive or electromechanical application devices.
In one embodiment, the parking brake is adjusted in steps in previously definable ranges during the process step of activating the electric parking brake. It is also contemplated that, by means of the performance parameters determined in the process step of the determining, monitoring and analyzing of performance parameters, a corresponding assist torque of the electric motor is calculated for assisting or implementing the stepped ranges of the parking brake. This calculation can, for example, take place in a hybrid drive control unit or in an electric motor control unit.
In addition, the electric parking brake is constructed such that it has a bistable behavior in the parked condition, whereby, when the electric supply fails, the electric parking brake is locked or released corresponding to a predetermination by the hybrid drive control unit, another assigned control device, or a driver's intention.
In the case of a trailer operation, a braking system of at least one trailer of the vehicle can be synchronously activated in the event of a braking prompt.
The previously definable operating conditions of the vehicle may, for example, be a start-stop operation, an emergency running function in the case of a circuit defect of the service brake and/or an emergency running function in the case of a defective service brake pedal.
In a preferred embodiment, the internal-combustion engine is constructed as a diesel engine.
The electric motor may be arranged in a parallel or serial position with respect to the internal-combustion engine. The performance parameters vehicle speed, wheel speed, status of the service and parking brake, data of the electric motor control unit and of the internal-combustion engine control unit are monitored, determined and analyzed. These data are, for example, available on a bus, such as a CAN bus.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.